This invention relates to methods and apparatus for transmitting data messages in such a way that interception is virtually impossible.
With the increased use of the Internet, and especially of the Internet as used to transmit broadband data signals, the necessity for avoiding unauthorized interception of such messages becomes ever more critical. Methods have been proposed using a decryption key which is reliably transported to a destination. A message that has been encrypted using a corresponding encryption key, and sent over an interceptible medium, then requires that the message be decrypted by an authorized recipient, who has the key, or an unauthorized recipient, who does not have the key. Various encryption schemes have been proposed, but the ever increasing power of modern computers makes unauthorized decryption an ever increasing threat. Much of the information from the Internet will be broadcast into a plurality of homes over a shared medium such as a co-axial cable, an optical fiber cable, or wireless, having the characteristic that it is easy for unauthorized recipients to intercept the raw signal that is not destined for them. A problem of the prior art, therefore, is that it is difficult to prevent unencrypted signals which are broadcast to a plurality of destinations from being illegally intercepted by an unwanted destination; even intercepted encrypted messages may no longer be safe from decryption by unwanted users.
The above problem is solved, and an advance is made over the prior art in accordance with this invention wherein a fraction of the data that is to be transmitted from a source to a destination is withheld from a broadcast medium, and is instead transmitted over a more secure and private medium such as a telephone connection; the data received over the broadcast medium is then combined with the data that had been withheld from the broadcast medium, but transmitted over the secure medium in order to derive the complete data message. Advantageously, such an arrangement makes decryption essentially impossible since the interceptor cannot access the full data of the data message. In many cases, the secure connection exists as an upstream connection for controlling the source of the data message; by using this upstream connection as a two-way connection, a separate downstream connection is conveniently formed to convey the data that had been withheld from the broadcast medium.
In accordance with one embodiment of the invention, the full data is first scrambled before a regular and repetitive portion of the data is extracted to be withheld from the broadcast medium, and to be transmitted over the secure medium. Advantageously, such an arrangement makes partial decryption much more difficult.